Scaling QPixmap image

Article Metadata

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Tested with

Devices(s): Nokia 5800 XpressMusic

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Compatibility

Platform(s): S60 5th Edition

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Article

Keywords: QPixmap

Created: tepaa (26 Mar 2009)

Last edited: hamishwillee (11 Oct 2012)

Overview

This code snippets shows how to scale a QPixmap image.

Preconditions

• Install latest Nokia Qt SDK

Header

public:
    void updateImage(); 
    void paintEvent(QPaintEvent*);
    void resizeEvent (QResizeEvent*);
 
private: //Data
    QPixmap*         pixmap;
    QSize widgetSize;

Source

The application supports screen orientation changes. In resizeEvent(), store the new size of the widget. This way the image can always be scaled to the correct size.

void QMyWidget::resizeEvent (QResizeEvent* event)
    {
    widgetSize = event->size();
    // Call base class impl
    QWidget::resizeEvent(event);
    }

Load the image from the file system:

void QMyWidget::updateImage()
    {
    delete pixmap;
    pixmap = 0;
    // imagePath can be something like "c:/data/Images/myImage.jpg"
    pixmap = new QPixmap(imagePath);
    update();
    }

Scale the new image and draw it on the screen.

void QMyWidget::paintEvent(QPaintEvent *)
    {
    QPainter painter(this);
 
    if (!pixmap->isNull())
        {
        QPoint centerPoint(0,0);
        // Scale new image which size is widgetSize
        QPixmap scaledPixmap = pixmap->scaled(widgetSize, Qt::KeepAspectRatio);
        // Calculate image center position into screen
        centerPoint.setX((widgetSize.width()-scaledPixmap.width())/2);
        centerPoint.setY((widgetSize.height()-scaledPixmap.height())/2);
        // Draw image
        painter.drawPixmap(centerPoint,scaledPixmap);
        }
    }

Postconditions

The QPixmap image has been scaled.

Related articles

Scaling QGraphicsPixmapItem